Many lower body aerobic exercise apparatus are known in the art, including treadmills, stationary cycles, ski machines and stair steppers.
Treadmills, such as that disclosed in U.S. Pat. No. 5,484,362, typically include an endless belt supported on a platform. To use a treadmill, the user walks or runs on the belt as it is rotated along the surface of the platform. The rotation of the belt is controlled by a motor and often the incline of the platform (and the belt) may be adjusted in order to simulate walking or running uphill. The user is not, however, typically able to adjust a resistance force (other than by increasing the incline) since the belt is turned by the motor rather than by the user. Another drawback of treadmills is that the user's feet repeatedly pound down onto the belt surface thereby causing harmful stress to the user's joints, similar to that experienced when running outdoors.
Stationary cycles offer the user the option of a variable resistance through various means well known in the art. These resistance mechanisms include vaned wheel assemblies (similar to fans), flywheels in combination with a friction application device such as brake pads or a belt, and alternators which vary the resistance in response to an electrical signal. In addition, some stationary cycles may include an upper body exercise portion. One such example, disclosed in U.S. Pat. No. 4,880,225, includes a pair of handlebars pivotally connected to the frame of the cycle and operably connected to the pedals so as to reciprocate back and forth in response to, and proportionally to the pedal movement. All stationary cycles suffer from the same drawback, however, in that the leg movement is limited to the predefined circular path of the pedals.
Ski machines offer variable resistance and variable range of motion while avoiding the undesirable stress to the joints by allowing the user to simulate a cross-country skiing type motion. This is typically accomplished, as shown in U.S. Pat. No. 5,387,168, by slidably mounting a pair of foot supports to a base. Optionally, an upper body exercise apparatus may also be included. Because of the unnatural straight reciprocating movement, many users find that exercise machines of this type are awkward to use, and often require a significant learning curve. In addition, a pad or belt, such as that taught by the '168 patent, is required to stabilize the midsection of the user's body, further contributing to the awkward feel of the machine.
In recent years stair stepper type exercise machines have become particularly popular. A typical stair stepper machine, such as that disclosed in U.S. Reissue Pat. No. 34,959, includes a pair of foot pedals, each mounted to one end of a respective arm. The arms, in turn are pivotally mounted at their other ends to a stationary frame. The arms may be operably connected together so as to restrict movement to being 180.degree. out of phase, or, as in the case of the '959 patent, may be independently moveable. In either case, various resistance mechanisms may be employed, including alternators, friction clutches or linear resistance devices such as hydraulic or pneumatic cylinders. In use, the pivot point of the arms is in front of and below the user. Accordingly, the arc defined by the pedal movement is significantly different from the natural walking motion.